Amoxicillin is approved for treating the above infections only when they are caused by certain types of bacteria. Not all bacteria will respond to amoxicillin. Also, bacteria have different resistance patterns in different regions in the country. This means that some bacteria may be susceptible to amoxicillin in certain parts of the country but not in others. Amoxicillin is completely ineffective for treating viral illnesses (such as the common cold
or the flu
In some situations, your healthcare provider may perform certain tests to see if your particular infection is susceptible or resistant to amoxicillin. In other situations, your healthcare provider may decide to try amoxicillin without such tests, especially for infections that are not severe.
It is important to note that a high percentage of people with mononucleosis
("mono") who take antibiotics similar to amoxicillin develop a skin rash. Therefore, amoxicillin is not recommended for use in people with mononucleosis.